feat(p1): add daily snapshots and fan tracking

Implement P1: seven-metric view snapshots, relation/stat fan snapshots, failure placeholders, resume by daily completion markers, Cookie login warnings, daily SQLite backups, Shanghai daily scheduling, and CLI snapshot/auth-check commands. Real read-only run captured 795/795 videos successfully over 1124s with a verified daily backup.

reaction_board/timeutil.py

@@ -0,0 +1,59 @@
+# -*- coding: utf-8 -*-
+"""上海时区与每日任务时间计算。
+
+B 站数据口径使用 ``Asia/Shanghai``。中国自 1991 年起不再使用夏令时，因此这里
+用固定 UTC+8，避免 Windows 上依赖未安装的 ``tzdata`` 包。
+"""
+
+from __future__ import annotations
+
+import re
+import time
+from datetime import datetime, timedelta, timezone
+
+SHANGHAI_TZ = timezone(timedelta(hours=8))
+_HHMM_RE = re.compile(r"^([01]\d|2[0-3]):([0-5]\d)$")
+_DATE_RE = re.compile(r"^\d{4}-\d{2}-\d{2}$")
+
+
+def shanghai_datetime(ts: float | None = None) -> datetime:
+    return datetime.fromtimestamp(time.time() if ts is None else ts, SHANGHAI_TZ)
+
+
+def shanghai_date(ts: float | None = None) -> str:
+    return shanghai_datetime(ts).strftime("%Y-%m-%d")
+
+
+def parse_hhmm(value: str) -> tuple[int, int]:
+    match = _HHMM_RE.match(value or "")
+    if not match:
+        raise ValueError(f"时间必须是 HH:MM（24 小时制）: {value!r}")
+    return int(match.group(1)), int(match.group(2))
+
+
+def next_daily_run(now: float, hhmm: str) -> float:
+    """返回 ``now`` 之后（严格大于）最近的 ``hh:mm`` 上海时间时间戳。"""
+    hour, minute = parse_hhmm(hhmm)
+    current = shanghai_datetime(now)
+    target = current.replace(hour=hour, minute=minute, second=0, microsecond=0)
+    if target.timestamp() <= now:
+        target += timedelta(days=1)
+    return target.timestamp()
+
+
+def is_date(value: str) -> bool:
+    if not _DATE_RE.match(value or ""):
+        return False
+    try:
+        datetime.strptime(value, "%Y-%m-%d")
+    except ValueError:
+        return False
+    return True
+
+
+def day_bounds(date: str) -> tuple[float, float]:
+    """返回上海时区某一天的 [start, end) 时间戳。"""
+    if not is_date(date):
+        raise ValueError(f"日期格式必须是 YYYY-MM-DD: {date!r}")
+    start = datetime.strptime(date, "%Y-%m-%d").replace(tzinfo=SHANGHAI_TZ)
+    return start.timestamp(), (start + timedelta(days=1)).timestamp()